Wasps of the cosmopolitan genus Polistes (the only genus in the tribe Polistini) are the most familiar of the polistine wasps, and are the most common type of paper wasp in North America. It is also the single largest genus within the family Vespidae, with over 300 recognized species and subspecies. Their innate preferences for nest-building sites leads them to commonly build nests on human habitation, where they can be very unwelcome; although generally not aggressive, they can be provoked into defending their nests. All species are predatory, and they may consume large numbers of caterpillars, in which respect they are generally considered beneficial. The European paper wasp, Polistes dominula, was introduced into the US about 1981 and has quickly spread throughout most of the country, in most cases replacing native species within a few years. This species is very commonly mistaken for a yellowjacket, as it is black, strongly marked with yellow, and quite different from the native North American species of Polistes. The cuckoo wasp, Polistes sulcifer, is an obligate social parasite, whose only host is P. dominula.[2]Polistes annularis, whose species name is Latin for "ringed," is also known for its distinctive red body color.[3]Polistes metricus adults malaxate their insect prey by chewing them into a pulp, sucking out and ingesting the body fluids, then feed the rest of the morsel to their larvae.[4] The most widely distributed South American wasp species, Polistes versicolor is particularly common in the Southeastern Brazilian states. This social wasp is commonly referred to as the Yellow Paper wasp due to the distinct yellow bands found on its thorax and abdomen.[5]Polistes wasps can be identified by their characteristic flight; their long legs dangle below their bodies, which are also more slender than a yellowjacket.[6]

Life cycle[edit]

The general life cycle of Polistes can be divided into four phases:[7]

Founding (or pre-emergence) phase

Worker phase

Reproductive phase

Intermediate phase

Founding (or pre-emergence) phase[edit]

The founding stage begins in the spring when a solitary female (the "foundress") or a small group of related females initiates the construction of a nest. The wasps begin by fashioning a petiole, a short stalk which will connect the new nest to a substrate (often the eave of a house or outbuilding), and building a single brood cell at the end of it. Further cells are added laterally in a hexagonal pattern, each cell surrounded by six others. Although nests can achieve impressive sizes, they almost always maintain a basic shape: petiolated (stellocyttarous), single-combed, unprotected, and open (gymnodomous).

Eggs are laid by the foundress directly into the brood cells and are guarded by the foundress and the assisting females (if present). After the first larvae hatch, the foundress feeds them via progressive provisioning, bringing softened caterpillar flesh to the larvae multiple times throughout their development (as opposed to the one-time provisioning seen in some other hymenopteran groups). Each of this first seasonal brood of new paper wasps is exclusively female and destined to a subordinate worker position inside the nest; they do not found their own nests and instead assist their mother in the care and maintenance of future sisters.

Some foundress wasps do not build their own nests, but rather attempt to usurp that of another female. These usurpation attempts may or may not be successful, but almost always result in impressive displays of aggression and violence. Females may also adopt a more peaceful alternative reproduction strategy by joining the nest of a close relative (usually a sister) and working as assisting females (see above). In the latter case, evidence shows such cofounding females are generally, but not exclusively, close relatives.[7]

Worker phase[edit]

The worker phase usually begins in the early summer, roughly two months after colony initiation, with the emergence of the first workers. These new females take up most of the colony's work duties, foraging, caring for brood, and maintaining the structure of the nest. Around this time, those females which assisted in nest foundation (if present) are driven from the nest by aggressive behavior on the part of the foundress, and leave either to start their own late-season nests or usurp another's.

Reproductive phase[edit]

The reproductive phase of the colony begins when the first female reproductives (the gynes) emerge from their brood cells. These reproductives differ from their worker sisters by having increased levels of fat stores and cryoprotectant carbohydrate compounds (allowing them to survive the over-wintering period). These reproductives will contribute genes directly to the next generation, while their worker sisters will normally pass along their genes indirectly.

Intermediate phase[edit]

Once male reproductives emerge and both males and females disperse from the natal nest for mating flights, the so-called intermediate phase begins. Brood care and foraging behavior decline and worker numbers drop as dying individuals are no longer replaced by new ones. Intracolonial aggression increases and the social cohesion of the nest declines. In temperate Polistes species, individuals (almost exclusively inseminated females) gather in groups of up to 50 individuals and seek a sheltered location (called a hibernaculum) in which to over-winter.

Behavior[edit]

Dominance hierarchy system[edit]

Morphologically, the foundress and subordinate reproductive members of the colony differ little. However, several studies have shown behavioral differentiation occurs among females both between and within generations. For example, in the species Polistes humilis the queen displays a "tail wagging" behavior to assert her dominance over the worker class.[8] Similarly,in P. dominula, Polistes canadensis also possesses behavioral differentiation between the queen and her nestmates, with the queen often suppressing the aggressive behavior of subordinates through lateral abdominal vibrations and stroking. In contrast, unmated females are nonaggressive.[9] In Polistes exclamans queens have different amounts of glucose, fructose and trehalose which lead to different cryoprotectant levels. This alters their survivability in different temperatures, increasing their odds of reproduction. Females in P. bellicosus are also morphologically similar between caste separations. For example, a P. bellicosus worker could become queen, and egg-layer, if all of the original foundresses die or leave the nest.[10] This is also true for Polistes dorsalis, which is another species that displays dominant behavior. Despite having no distinct morphological caste, roles of P. dorsalis tend to be fixed in a system with division of labor.[11]

Nestmate recognition[edit]

Polistes spp. discriminate colony mates using an acquired (i.e. learned) cue, absorbing hydrocarbons from the natal nest at eclosion.[12] This cuticular hydrocarbon "signature" is derived both from the plant material and the foundress-applied substances from which the nest is made. Studies of Polistes fuscatus have researched the molecular basis of the recognition "pheromone" used by the wasps, and indicate at least some of the recognizable labels have the same chemical constituents as the adult cuticular hydrocarbons. Similar recognition is found in Polistes metricus.

Dominant individuals of P. dominula have differing cuticular profiles to workers,[13] and the frequent observations of the dominant female stroking its gaster across the nest surface, combined with its staying on the nest for longer times than subordinates, suggests the dominant individual may contribute more to the nest odor.

A study of P. carolina showed females do not preferentially feed their own progeny (as larvae),[14] so it may be the case that nest odor only serves as a likely indicator of relatedness, rather than a specific label of kinship.[citation needed]

Further to this recognition of nestmates, a study on Polistes biglumis illustrated how foundresses discriminate between 'alien' eggs and their own, via differential oophagy.[15]

The mechanism of differentiation was not elucidated, but was thought to be based upon differences in cuticular hydrocarbon odor. Whether the discriminatory oophagy was a result of decreased tolerance of alien odors during the later, reproductive phase of the colony cycle, or an actual discrimination between worker- and reproductive-destined eggs, remains to be supported with good evidence.[citation needed]

Within the Polistes family, there are three known social obligate parasites: P. sulcifer, P. atrimandibularis, and P. semenowi, whom parasitize other Polistes wasps. Known host species of these parasites are P. dominulus, P. gallicus, P. nimphus, P. associus, and P. biglumis.[19] Although these parasites differ in their host invasion strategies, their end goal is to successfully infiltrate the host nest and reproduce at the host's expense.